I am not positive on the 1985 tanks, however the newer black ones are ABS. Solvent weld compounds work on them.
If you cannot find out for sure, maybe try some solvent weld cement on a location that is not so critical. If it starts melting like it should, then your odds of a good repair are higher.
Current Sunlines: 2004 T310SR, 2004 T1950, 2004 T2475, 2007 T2499, 2004 T317SR
Prior Sunlines: 2004 T2499 - Fern Blue
2005 Ford F350 Lariat, 6.8L V10 W/ 4.10 rear axle, CC, Short Bed, SRW. Reese HP trunnion bar hitch W/ HP DC
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